Switch

ABSTRACT

A switch includes an input terminal, an output terminal, and a stack including transistors, such as, for example, field effect transistors, coupled in series, the stack being coupled between the input terminal and the output terminal. The switch also includes at least one switching element configured to be selectively operated in a conducting state or a non-conducting state, and at least one overvoltage protection element coupled to the stack by the at least one switching element. By way of example, the switch can implement a radio-frequency switch.

TECHNICAL FIELD

Various embodiments relate to a switch comprising an input terminal, anoutput terminal, and a stack comprising transistors coupled in series,the stack being coupled between the input terminal and the outputterminal. The switch also comprises at least one switching element,which can selectively be operated in a conducting state or anon-conducting state, and at least one overvoltage protection elementcoupled to the stack via the at least one switching element.

BACKGROUND

Radio-frequency (RF) switches are used in a multiplicity of RF circuitsin order to implement different functions. Resonant circuits can be setfor resonance operation for example by means of an RF switch. Suchresonant circuits can be used for example as antennas in mobilecommunication devices.

In detail, for example, a communication system that uses differentfrequencies for different signalling methods can be implemented using anetwork of RF switches. The RF switches can be used to select betweendifferent types of RF front-end circuits. One example of such acommunication system is a multi-standard mobile telephone that can carryout telephone calls using different standards, such as, for example,Third Generation Partnership Project (3GPP) Code Division MultipleAccess (CDMA) or 3GPP Global System for Mobile Communications (GSM) or3GPP Long Term Evolution (LTE). One and the same communication standard,moreover, can use different frequencies e.g. depending on the networkoperator. Using an RF switch, an RF front-end circuit optimized for CDMAcommunication can be used for CDMA telephone calls; while an RFfront-end circuit optimized for GSM communication can be used for GSMtelephone calls.

Furthermore, RF switches can be used to implement settable matchingnetworks for antennas or power amplifiers. In this way it is possible toprovide settable adjustment of RF filters by connection anddisconnection and/or bypassing of passive matching and setting elements.

In order to provide RF switches having a particularly high dielectricstrength, techniques are known which use a stack comprising field effecttransistors (FETs) coupled in series. Typical dielectric strengths forswitches are e.g. in the region of 24 V for 50-ohm mobile radioapplications and up to 100 V on antenna resonant circuits for an openstate of the switch. Since the individual components of typicalproduction techniques such as, for example, the complementary metaloxide semiconductor (CMOS) process are not designed for such highvoltages, the stacked arrangement of a multiplicity of FETs is used. Thevoltage can then be distributed among the multiplicity of FETs, suchthat each individual FET is exposed only to a lower voltage. By way ofexample, individual FETs in a CMOS silicon-on-insulator (SOI) processtypically have a maximum dielectric strength between source contact anddrain contact of 2.5 V. 40 FETs, for example, are then stacked in orderto obtain the dielectric strength of 100 V; see U.S. Pat. No. 4,317,055,for example, for corresponding techniques.

However, such RF switches have certain disadvantages and/or limitations.By way of example, it may be possible that a lower limiting frequencyfor the voltage change at the input terminal exists for a specificdimensioning of the components used; see Shifrin, Mitchell B., Peter J.Katzin, and Yalcin Ayasli. “Monolithic FET structures for high-powercontrol component applications.” IEEE Trans. Microwave Theory andTechniques, 37 (1989) 2134-2141; equations 12, 14 and 15. If the voltageat the input terminal varies with a frequency that is lower than saidlimiting frequency, damage to the FETs used can occur. The switch canthus become unusable.

A slow variation of the voltages over time can often occur inassociation with electrostatic discharge (ESD).

U.S. Pat. No. 8,461,903 B1 discloses techniques in which comparativelyfast switchover times can be achieved despite a conservativedimensioning of the components used—and thus an improved robustness visà vis ESD events. However, a corresponding switch can be comparativelycomplicated and costly in terms of production. Moreover, a correspondingswitch typically requires a PMOS transistor; however, a correspondingtransistor is not available in various production techniques, with theresult that such techniques cannot be usable or can be usable only to alimited extent.

SUMMARY

Various embodiments relate to a switch comprising an input terminal, anoutput terminal, and a stack comprising transistors coupled in series,said stack being coupled between the input terminal and the outputterminal. The switch also comprises at least one switching element,which can selectively be operated in a conducting state or anon-conducting state, and at least one overvoltage protection elementcoupled to the stack by means of the at least one switching element.

Various embodiments relate to selectively activating, using at least oneswitching element, an overvoltage protection element coupled to a stackcomprising transistors coupled in series.

The features set out above and features described below can be used notonly in the corresponding combinations explicitly set out, but also infurther combinations or in isolation, without departing from the scopeof protection of the present invention.

Those skilled in the art will recognize additional features andadvantages upon reading the following detailed description, and uponviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

The elements of the drawings are not necessarily to scale relative toeach other. Like reference numerals designate corresponding similarparts. The features of the various illustrated embodiments can becombined unless they exclude each other. Embodiments are depicted in thedrawings and are detailed in the description which follows.

FIG. 1 illustrates two RF switches which are used in interaction with anLC resonant circuit in the form of an antenna tuning.

FIG. 2 schematically illustrates the construction of an RF switch inaccordance with reference implementations.

FIG. 3 schematically illustrates the construction of an RF switch withan overvoltage protection element in accordance with variousembodiments.

FIG. 4 schematically illustrates the construction of an RF switch inaccordance with various embodiments, wherein the RF switch comprises aplurality of overvoltage protection elements which are assigned todifferent FETs of the RF switch and each comprise two capacitors.

DETAILED DESCRIPTION

The above-described properties, features and advantages of thisinvention and the way in which they are achieved will become clearer andmore clearly understood in association with the following description ofthe exemplary embodiments which are explained in greater detail inassociation with the drawings.

The present invention is explained in greater detail below on the basisof preferred embodiments with reference to the drawings. In the figures,identical reference signs designate identical or similar elements. Thefigures are schematic representations of various embodiments of theinvention. Elements illustrated in the figures are not necessarilyillustrated in a manner true to scale. Rather, the various elementsillustrated in the figures are rendered in such a way that theirfunction and general purpose becomes understandable to the personskilled in the art. Connections and couplings between functional unitsand elements as illustrated in the figures can also be implemented asindirect connection or coupling. A connection or coupling can beimplemented in a wired or wireless manner. Functional units can beimplemented as hardware, software or a combination of hardware andsoftware.

A description is given below of techniques for implementing anelectronic switch. The switch can switch electrical current flow and/orvoltage. In particular, a description is given of techniques forimplementing an RF switch suitable for switching a radio-frequencyvoltage. In this case, RF may denote for example such frequencies thatare greater than 800 MHz, or are >1 GHz or are >2 GHz.

A description is given below of techniques for implementing an RF switchwhich is particularly robust vis à vis ESD events.

Typically, such states in which a low-frequency voltage having asignificant amplitude is present on account of a discharge, for example,can be designated as an ESD event. By way of example, an ESD event canbe caused on account of the manual handling of a corresponding RFswitch. ESD events can have e.g. frequencies in the range of a few MHz,i.e. significantly lower frequencies than RF. ESD events can bedescribed by a wide variety of models. One example of a correspondingmodel is the so-called human body model (HBM).

The switch can comprise for example a stack comprising transistorscoupled in series. In this configuration, a limited dielectric strengthof individual transistors of the stack can be compensated for by theseries connection of a plurality of transistors.

Reference is primarily made below to examples in which the transistorsare implemented by FETs. Examples of FETs are e.g.:metal-oxide-semiconductor FETs (MOSFETs); junction field effecttransistor (JFET); high-electron-mobility transistor (HEMT); Schottkyfield effect transistor or metal-semiconductor field effect transistor(MESFET); insulated gate field effect transistor (IGFET);metal-insulator-semiconductor field effect transistor (MISFET); organicfield effect transistors (OFET); and chemically sensitive field effecttransistors (ChemFET). In other examples, however, the transistors canalso be implemented e.g. by bipolar transistors.

In various examples, the switch comprises an overvoltage protectionelement. The overvoltage protection element is connected to the stack bymeans of a switching element. The switching element can selectively beoperated in a conducting (i.e. closed) state or a non-conducting (thatis to say open) state. By way of example, the switching element could beimplemented by a transistor, for instance a FET.

The invention is based on the insight that, with regard to protectionfrom ESD events, it is possible to differentiate between differentoperating modes. By way of example, ESD events may occur with increasedprevalence during the production of the switch. During the production ofthe switch, the switch may be subjected to various handling steps.Therefore, ESD events may occur particularly frequently. Therefore, theESD protection may be particularly necessary precisely duringproduction. On the other hand, during operation by the end user, the ESDprotection may not be necessary or may be necessary only to a limitedextent. This may be the case since the switch may be embedded into ahousing during intended operation, which provides ESD protection on astructural basis. Moreover, during intended operation, the switch may bearranged on a printed circuit board having further passive electroniccomponents. These passive components often implement a protectionfunctionality vis à vis ESD events.

The switching element and/or the coupling of the overvoltage protectionelement to the stack by means of the switching element may be configuredto selectively switch on and off the ESD protection functionality of theovervoltage protection element for the stack. As a result, it may bepossible for operation that is optimized in relation to the ESDprotection functionality to be implemented. The ESD protectionfunctionality may be selectively enabled or disabled. During anoperating mode which is particularly exposed in relation to ESD events,the switching element can be operated in a state which has the effectthat the overvoltage protection element can manifest its ESD protectionfunctionality for the stack; during a further operating mode, which isnot particularly exposed in relation to ESD events, the switchingelement can be operated in a state which has the effect that theovervoltage protection element cannot manifest its ESD protectionfunctionality for the stack, but the other characteristic variables—suchas switching speed, dielectric strength, channel resistance, capacitancein the non-conducting state, and/or linearity, etc.—of the switch arenot adversely influenced. The RF performance characteristic of the RFswitch may be particularly good.

Depending on the implementation of the coupling between the switchingelement and the overvoltage protection element, the ESD protectionfunctionality can be provided by the overvoltage protection element forthe stack in the conducting or non-conducting state of the switchingelement.

FIG. 1 shows a system 170, comprising two RF switches 100A, 100B. Eachof the RF switches 100A, 100B can be embodied in accordance with thetechniques described herein.

The system 170 comprises a metal conductor 96, which can be embodied asinductance for an LC resonant circuit 197. An RF signal 96A is fed intothe metal conductor 96. The metal conductor 96 is coupled to ground ineach case via two differently dimensioned capacitors 97 and assignedswitches 100A, 100B. The metal conductor 96 and the capacitors 97 formthe LC resonant circuit 197. The LC resonant circuit 197 can implementan antenna, for example; in this case, the antenna acts as a resonancereservoir.

In this case, the switches 100A, 100B can be operated in a closed stateor an open state. In the open state, a low conductivity is present(non-conducting state); in the closed state, a high conductivity ispresent (conducting state). Depending on the state in which the switches100A, 100B are operated, a different capacitor 97 interacts with theconductor track 96; in this way, resonant operation of the LC resonantcircuit can be achieved for different frequencies. The resonantoperation enables a high transmission power and energy-efficientoperation for the respectively activated frequency band.

In this case, the switches 100A, 100B are part of an electrical circuit160 that also comprises a charge pump 163, a driver 162 and a voltageregulator 161. The driver 162 is used to operate the switches 100A, 100Bin each case selectively in the conducting or non-conducting state. Thedriver 162 therefore implements control functionality. The charge pump163 provides the charge for the switching. The charge pump 163 canoptionally also apply negative voltage to the substrate. The voltageregulator 161 controls the components 162, 163.

FIG. 2 illustrates an RF switch 80 in accordance with a referenceimplementation. The RF switch 80 comprises a stack 110 comprising aplurality of FETs 111. The FETs 111—for example N-channel FETs—areconnected in series; the RF switch 80 thus comprises a series connectionof the FETs 111. In this case, a respective source contact 106 iscoupled to the drain contact 105 of the respectively adjacent FET 111;the state of the FET 111 is controlled via the gate contact 107 (cf.inset in FIG. 2; the inset is enclosed by a dashed border in FIG. 2).

The LC resonant circuit 197 is connected to the input terminal 101.Ground is connected to the output terminal 102.

Resistors 112 are provided between the drain contacts 105 and the sourcecontacts 106. The resistors 112 have high resistances, i.e. have forexample resistance values in the range of 20-40 kohms. The resistors 112prevent undefined floating of the potentials of the source contacts 106and drain contacts 105 of the various FETs 111 in the non-conductingstate.

A driver 135 is coupled to the gate contacts of the various FETs 111 viagate contact resistors 115, 116. The gate contact resistors 115, 116 andthe gate capacitances of the gate contacts 107 define the time constantof the respective FET 111:τ=RC,  (1)

wherein R defines the value of the respective gate contact resistor 115,116; and C defines the value of the respective gate capacitance. Thegate capacitance is typically proportional to the gate width. A furtherinfluencing factor for the gate capacitance may be the gate length.Typical gate widths for a FET may be e.g. in the range of 4-6 mm,wherein e.g. 4 sets each of 100 FET fingers are used here per FET 111,wherein each finger in turn has a gate width of 15 μm. Typical gatelengths for a FET may be e.g. in the range of 10-500 nm, e.g. in therange of 100-120 nm.

In principle, a faster switchover, i.e. a smaller time constant or atime constant corresponding to a shorter time, is worthwhile here. Onthe other hand, a faulty behaviour or damage of one or more of the FETs111 may occur in association with comparatively small time constants forslow ESD events. In particular, a non-uniform distribution of thevoltage via the various FETs 111 may occur in this case. This isexplained below.

If a slow voltage pulse—i.e. with a frequency spectrum significantlybelow RF—is present at the input terminal 101: as a result of aparasitic capacitive coupling between the drain contact 105 and the gatecontact 107 of the FET 111 adjacent to the input terminal 101 (said FETbeing illustrated at the very top and highlighted by the arrow in FIG.2), this topmost FET 111 is opened; however, on account of thecomparatively small time constant, the charge flows away from the gatecontact 107 rapidly via the gate contact resistor 115, 116 and said FET111 closes again. As a result, a particularly high voltage is presentbetween the drain contact 105 and the source contact 106 of the topmostFET 111; this voltage can be greater than the breakdown voltage that canbe present in the non-conducting state between drain contact 105 andsource contact 106. The FET 111 can be damaged as a result.

For a quantitative explanation of this effect, see the abovementionedpublication by Shifrin, Mitchell B. et al.: equ. 15.

A description is given below of how an effective ESD protection can beachieved despite a small dimensioning of the time constants for the FETs111. A description is given below of, in particular, techniques whichenable efficient ESD protection without significant reduction of the RFperformance characteristic of the RF switch 100.

FIG. 3 illustrates aspects with regard to an overvoltage protectionelement 210. The overvoltage protection element 210 provides an ESDprotection functionality for the stack 110.

In the example in FIG. 3, the overvoltage protection element 210 isillustrated schematically by two oppositely biased diodes 516, 517. Ingeneral, however, it is also possible to use other implementations forthe overvoltage protection element 210. One example is particular formsof NPN or PNP protection transistors. The latter can comprise a stagecollector, for example. The collector current and/or emitter current canthereby be limited. A further example concerns diodes on an insulatorsubstrate or else ESD polymer diodes. A further example concernsinductances that represent a short circuit at low frequency. It is clearfrom the above that many different examples can be chosen for theovervoltage protection element 210.

The overvoltage protection element 210 is connected to the stack 110 bymeans of a switching element 211. In the example in FIG. 3, theovervoltage protection element 210 is connected to the stack 110 inparticular in series connection with the switching element 211. In otherexamples, other couplings of the overvoltage protection element 210 tothe stack 110 and the switching element 211 are possible.

While the switching element 211 is illustrated as part of theovervoltage protection element 210 in the example in FIG. 3, in otherexemplary implementations it may also be possible for the switchingelement 211 to be implemented separately.

The functioning of the switch 100 is explained in greater detail below.In particular, the functioning of the switching element 211 in relationto the ESD protection functionality provided by the overvoltageprotection element 210 is explained in greater detail below.

The switching element 211 can be selectively operated in a conductingstate or a non-conducting state. This means that the overvoltageprotection element 210 selectively provides the ESD protectionfunctionality, depending on the operating mode of the switching element211. As a result, it may be possible to selectively operate the switch100 in a first operating mode optimized in relation to the ESDprotection functionality, and in a second operating mode optimized inrelation to the RF performance characteristic of the switch 100.

In the example in FIG. 3, the switching element 211 is switcheddepending on a value of the supply voltage VDD present at a supplyterminal 236. By way of example, if the intended supply voltage ispresent at the supply terminal 236—that is to say that the value of thesupply voltage assumes for example VDD=+5 V—the switching element 211can be operated in the non-conducting state. As a result, the diodes516, 517 are not coupled to the stack 110; as a result, no ESDprotection functionality is provided, but at the same time the RFperformance characteristic of the switch 100 is not reduced by thediodes 516, 517. If the value of the supply voltage is close to, forexample, VDD=0 V, the switching element can be operated in theconducting state. As a result, the diodes 516, 517 are coupled to thestack 110; as a result, the ESD protection functionality is provided,but at the same time the RF performance characteristic of the switch 100is reduced by the diodes 516, 517. Since a value of VDD=0 V of thesupply voltage is typically not present during intended or normaloperation of the switch 100, such a reduction of the RF performance ofthe switch 100 can be tolerated. By way of example, the supply voltagecan assume a value of VDD=0 V during the production of the switch 100.

FIG. 4 illustrates aspects with regard to an exemplary implementation ofthe overvoltage protection element 210. In this case, the switch 100 inaccordance with the example in FIG. 4 corresponds, in principle, to theswitch 80 in accordance with the example in FIG. 2: once again the stack110 comprising a plurality of FETs 111 coupled in series is present.

In the example in FIG. 4, an associated overvoltage protection element210 is assigned to each FET 111. Each overvoltage protection element 210is coupled to the assigned FET 111 of the stack 110 by means of acorresponding switching element 211. This means that the same number ofovervoltage protection elements 210 and FETs 111 and switching elements211 is present.

In the example in FIG. 4, the switching elements 211 are implemented byFETs. In general, however, it would be possible to implement theswitching elements 211 differently, for example by bipolar transistors,or other types of field effect transistors, etc. By way of example, theswitching elements 211 can be implemented by one of the followingelements: MOSFETs; JFETs; HEMTs; MESFETs; IGFETs; MISFETs; OFETs; andChemFETs.

The gate contacts of the switching elements 211 are once again coupledto the supply terminal 236 in the example in FIG. 4. This means that theswitching elements 211 are selectively operated in the conducting ornon-conducting state depending on the supply voltage VDD.

It is evident from FIG. 4 that each overvoltage protection element 210comprises a capacitor 216. Each capacitor 216 is coupled in series withthe respectively assigned switching element 211 between thecorresponding gate contact 107 and the source contact 106 of therespective FET 111 of the stack 110. In FIG. 4, the source contact ofthe FET that implements the respective switching element 211 is coupledto the corresponding capacitor 216; the drain contact of said FET iscoupled to the gate contact 107 of the respective FET 111 of the stack110. The capacitors 216 achieve—selectively in the conducting state ofthe switching element 211—an amplified capacitive coupling between thesource contact 106 and the gate contact 107 of the FETs 111 of the stack110.

Each overvoltage protection element 210 also comprises a capacitor 217coupled between the gate contact 107 and the drain contact 105 of therespectively assigned FET 111. The capacitors 217 achieve an amplifiedcapacitive coupling between the drain contact 105 and the gate contact107 of the FETs 111 of the stack 110.

The functioning of the overvoltage protection elements 210 is explainedbelow. If the magnitude of the value of the supply voltage VDD exceeds apredefined threshold value, the switching elements 211 are operated inthe conducting state. This means that the capacitors 216 connect thegate contact 107 to the source contact 106. As a result, an amplifiedcapacitive coupling between the gate contact 107 and the source contact106 is achieved (in addition to the parasitic capacitive coupling). Inthis case, the capacitive coupling is increased by the capacitance valueof the respective capacitor 216. In this case, it may be worthwhile forthe capacitance value of the respective capacitor to be not less than 1pF, optionally not less than 2 pF, further optionally not less than 10pF. A sufficiently strong capacitive coupling is achieved as a result.

By way of example, it would be possible for the capacitance value of therespective capacitor 216 to bring about an amplification of the inherentcapacitive coupling between the gate contact 107 and the source contact106 of the respective FET 111 by at least an additional factor of 0.5,optionally of at least 2, further optionally of 3.

For the case where the capacitance value of the respective capacitor 216is approximately equal to the capacitance value of the respectivecapacitor 217, a symmetrical capacitive coupling between the draincontact 105 and the gate contact 107, and also the source contact 106and the gate contact 107, is present. This brings about a linearcharacteristic curve of the switch 100: the voltage drop is distributeduniformly between the drain contact 105 and the gate contact 107 and thesource contact 106 and the gate contact 107 of the respective fieldeffect transistor 111. This means that the quality of the RF switch 100is not restricted or is not significantly restricted by the overvoltageprotection elements 210. If the switching elements 211 are conducting,the same capacitive coupling is thus obtained between the drain contact105 and the gate contact 107, and also the source contact 106 and thegate contact 107. The voltage division ratio remains unchanged and therespective FET 111 has the same switching threshold as without anovervoltage protection element 210. The switching threshold correspondsto attaining the threshold voltage.

In the case of an asymmetrical capacitive coupling between the draincontact 105 and the gate contact 107, and also the source contact 106and the gate contact 107, however, the voltage pulse is no longerdistributed uniformly between gate-source and gate-drain; this thereforeresults in operation of the FET 111 in the conducting state before thethreshold voltage is attained. Furthermore, an asymmetrical effectivecapacitive coupling between drain contact 105 and gate contact 107, onthe one hand, and source contact 106 and gate contact 107, on the otherhand, has the effect that the characteristic curve of the FET 111 isshifted in a frequency-dependent manner owing to Z=1/jwC. This, too,results in the transistor being switched on prematurely in the case of aradio-frequency voltage. This is typically undesirable.

However, if the magnitude of the value of the supply voltage VDD doesnot exceed the predefined threshold value, the switching elements 211are operated in the non-conducting state. By way of example, the valueof the supply voltage can be close to VDD=0 V if an integrated circuit(IC) comprising the switch 100 is switched off. The switch and aplurality of other active components which are coupled to the supplyterminal 236 are then fed no energy by the supply voltage VDD. Such astate can be, for example, during the manufacture of the switch 100 orof the IC.

Since in such a state the switching elements 211 are operated in thenon-conducting state, only the additional capacitance of the capacitor217 is present between the drain contact 105 and the gate contact 107.The capacitance of the capacitors 216 is switched off. In such a case, apositive ESD pulse generates a fast switch-on of the FETs 111 since thethreshold voltage is attained rapidly on account of the additionalcapacitive coupling provided by the capacitors 217. Damage on account ofexcessively high source-drain voltages is avoided as a result of therapid switch-on of the FETs 111. The FETs 111 are switched to theconducting state before the breakdown voltage is attained. Even duringthe discharge via the gate contact resistors 115, the FETs 111 remainconducting on account of the additional capacitive coupling provided bythe capacitors 217, such that damage is avoided.

As already mentioned, an asymmetrical capacitive coupling between draincontact 105 and gate contact 107, and source contact 106 and gatecontact 107, generates an undesirable non-linear behaviour via à vis theRF performance characteristic. By way of example, H2/H3 products can begenerated. In this case, H2 and H3 denote second- and third-orderharmonics, i.e. 2× fundamental frequency and 3× fundamental frequency.Such harmonics typically arise if a sinusoidal signal is cut off; thisis a typical behaviour of a switch that switches prematurely. Since theasymmetrical capacitive coupling is implemented only for vanishing orsmall magnitudes of the value of the supply voltage VDD, however, thisdoes not signify a limitation for normal operation.

With regard to FIG. 4 a scenario is illustrated in which a correspondingovervoltage protection element 210 is assigned to each FET 111 of thestack 110. In general, however, it would also be possible for just asingle one or some of the FETs 111 of the stack 110 to have acorresponding assigned overvoltage protection element 210. By way ofexample, it would be possible for at least the FET 111 (illustrated atthe very top and identified by the arrow in FIG. 4) arranged adjacent tothe input terminal 101 in the stack 110 to have an assigned overvoltageprotection element 210. This may be the case since the largest voltagesin the case of an ESD event typically occur at the FET 111 arrangedadjacent to the input terminal 101. A space-efficient ESD protectionfunctionality can be provided as a result.

In an example in which a respective overvoltage protection element 210is assigned to a plurality of FETs 111 (cf. FIG. 4), it would bepossible for the capacitance values of the capacitors 216, 217 fordifferent overvoltage protection elements 210 to be identical or tovary. By way of example, it would be possible for the capacitance valuesof the capacitors 216 for overvoltage protection elements 210 which areassigned to different FETs 111 to have a deviation with respect to oneanother of more than 2%, preferably more than 20%, particularlypreferably more than 50%. Alternatively or additionally, it would bepossible, for example, for the capacitance values of the capacitors 217for overvoltage protection elements 210 which are assigned to differentFETs 111 to have a deviation with respect to one another of more than2%, preferably more than 20%, particularly preferably more than 50%. Byvarying the capacitance values, on the one hand it is possible toachieve an efficient ESD protection functionality; on the other hand itis possible to prevent the RF performance characteristic of the switch100 from being reduced unnecessarily.

By way of example, it would be possible for such capacitors 216, 217which belong to overvoltage protection elements 210 which are assignedto FETs 111 of the stack 110 which are arranged closer to (further awayfrom) the input terminal 110 to have larger capacitance values (smallercapacitance values). What can be achieved as a result is that the RFperformance characteristic of the switch 100 is influenced comparativelylittle by the provision of additional capacitive couplings between draincontacts 105, source contacts 106 and respectively the gate contacts107; at the same time, however, a particularly efficient ESD protectionfunctionality is made possible.

In other examples, it would also be possible for the capacitance valuesof corresponding capacitors 216, 217 for overvoltage protection elements210 which are assigned to different FETs 111 to have a deviation withrespect to one another of less than 50%, preferably less than 20%,particularly preferably less than 2%. In this way it may be possible toimplement the capacitors 216, 217 particularly simply andspace-efficiently. It is possible to use the same geometry for differentcapacitors 216, 217.

The implementation of the stack 110 in accordance with FIG. 4 is by wayof example. The FETs 111 of the stack 110 could e.g. have additionalcapacitors (not illustrated in FIG. 4) connected between thecorresponding drain contacts 105 and source contacts 106.

These capacitors can bring about an additional capacitance between thedrain contacts 105 and source contacts 106 of the FETs 111 of the stack110; as a result, the voltage in the non-conducting state can bedistributed particularly symmetrically along the gate length of therespective FET 111. Non-linearities during the operation of the switch100 can be avoided as a result.

Specifically, for example, a capacitance of the substrate can bringabout additional non-linearities of the switch 100. Thesenon-linearities are typically reduced significantly by the use of an SOIprocess. In an SOI process, the substrate, for example silicon, iselectrically isolated by an insulator layer from the integratedstructures of the switch 100, in particular from the FETs 111. In orderto avoid an uncontrolled fluctuation (called floating) of the potentialof the switch 100, it is possible for an additional body bias resistorto be provided per FET 111, which fixes the FETs 111 at a definedpotential. It would alternatively or additionally also be possible touse a negative bias voltage for the substrate in order to switch off thesubstrate diodes and significantly reduce asymmetries as a result. Insuch cases, however, a significant parasitic contribution arises onaccount of the body bias resistor. This parasitic contribution can becompensated for by individual dimensioning of the capacitors 216, 217.

A description was given above, with regard to the examples in FIGS. 3and 4, of scenarios in which the switching elements 211 are operated inthe conducting or non-conducting state depending on the value of thesupply voltage VDD. In other examples, however, it would also bepossible to selectively operate the switching elements 211 in theconducting or non-conducting state depending on other variables. By wayof example, it would be possible for the switching elements 211 to beoperated in the conducting state or in the non-conducting statedepending on an operating mode of the switch 100. The operating mode ofthe switch 100 can be determined for example by one or a plurality ofstate variables of a control logic of the switch 100. Alternatively oradditionally, it would also be possible for the switch 100 to comprise auser interface—for example a contact pad, a pushbutton, etc.—which isconfigured to determine the operating mode by user input. It would alsobe possible for the at least one switching element 211 to be operated inthe conducting state or non-conducting state depending on the presenceof the RF signal 96A at the input terminal 101.

To summarize, a description was given above of techniques for providingan efficient ESD protection functionality for RF switches. Thesetechniques are based on the use of one or a plurality of overvoltageprotection elements which selectively provide the ESD protectionfunctionality.

Such techniques can be implemented in particular in association with anestablished CMOS process. More complicated technologies such as, forexample, GaN-based structures or micromechanical elements(micromechanical structure; MEMS) need not be used. By way of example,in contrast to U.S. Pat. No. 8,461,903 B1, no PMOS transistor isrequired. The required wiring outlay is limited; simple architecturesare possible. By way of example, in contrast to U.S. Pat. No. 8,461,903B1, complicated synchronization of the gate contacts during switchoveris not required; suppression of the RF voltage during switchover inorder to avoid damage is not necessary either. The PMOS transistor inaccordance with U.S. Pat. No. 8,461,903 B1 does not have the samecapacitance for the conducting and non-conducting states: As a result,the RF signal 96A can bring about non-linearities since positive andnegative half-cycles can experience different parasitic capacitances.Such disadvantages, too, can be avoided by means of the techniquesdescribed herein.

By using the overvoltage protection element, it is possible as necessaryto provide the ESD protection functionality. On the other hand—if theESD protection functionality is not required—the effect of theovervoltage protection element can be masked out, as a result of whichthe RF performance of the RF switch is not impaired or is only slightlyimpaired.

It goes without saying that the features of the above-describedembodiments and aspects of the invention can be combined with oneanother. In particular, the features can be used not only in thecombinations described, but also in other combinations or by themselves,without departing from the field of the invention.

A description was given above of various examples with regard toapplications in which the switch is implemented in a system comprisingan antenna that forms an LC resonant circuit. However, correspondingtechniques can also be implemented for other applications, such as e.g.a switching of matches at RF amplifiers (low noise amplifier, poweramplifier) or surface acoustic wave (SAW) and/or bulk acoustic wave(BAW) filters.

A description was given above of various examples with regard to FETswhich form different switching elements in each case in a stackedarrangement. In other examples, bipolar transistors, for example, couldalso be used instead of FETs.

In accordance with some embodiments, the following examples arepresented:

EXAMPLE 1

Switch (100) comprising:

-   -   an input terminal (101),    -   an output terminal (102),    -   a stack (110) comprising transistors (111) coupled in series,        said stack being coupled between the input terminal (101) and        the output terminal (102),    -   at least one switching element (211), which is configured to be        selectively operated in a conducting state or a non-conducting        state, and    -   at least one overvoltage protection element (210) coupled to the        stack (110) by means of the at least one switching element        (211).

EXAMPLE 2

Switch (100) according to Example 1, which furthermore comprises:

-   -   a supply terminal (236), which is configured to provide a supply        voltage,

wherein the at least one switching element (211) is operated in theconducting state or in the non-conducting state depending on a value ofthe supply voltage (VDD).

EXAMPLE 3

Switch (100) according to Example 2,

wherein the at least one switching element (211) is operated in theconducting state if the magnitude of the value of the supply voltage(VDD) exceeds a predefined threshold value.

EXAMPLE 4

Integrated circuit comprising:

-   -   the switch (100) according to Example 2, and    -   a plurality of components which are coupled to the supply        terminal (236) and are operated by the supply voltage.

EXAMPLE 5

Switch (100) according to Example 1,

wherein the at least one switching element (211) is operated in theconducting state or in the non-conducting state depending on anoperating mode of the switch (100).

EXAMPLE 6

Switch (100) according to Example 5, which furthermore comprises:

-   -   a user interface, which is configured to determine the operating        mode by user input.

EXAMPLE 7

Switch (100) according to Example 1,

wherein the at least one switching element (211) is operated in theconducting state or in the non-conducting state depending on thepresence of a radio-frequency signal (96A) at the input terminal (101).

EXAMPLE 8

Switch (100) according to Example 1,

wherein the at least one overvoltage protection element (210) is coupledat least to the transistor (111) arranged adjacent to the input terminal(101) in the stack (110).

EXAMPLE 9

Switch (100) according to Example 1,

wherein the switch (100) comprises a plurality of overvoltage protectionelements (210) and switching elements (211),

wherein each overvoltage protection element (210) is coupled to arespectively assigned transistor (111) of the stack (110) by means of acorresponding switching element (211).

EXAMPLE 10

Switch (100) according to Example 9,

wherein each overvoltage protection element (210) comprises at least onecapacitor (216, 217),

wherein the capacitance values of corresponding capacitors (216, 217)for overvoltage protection elements (210) assigned to differenttransistors (111) have a deviation with respect to one another of morethan 2%, preferably more than 20%, particularly preferably more than50%.

EXAMPLE 11

Switch (100) according to Example 9,

wherein the capacitance value of the capacitor (216, 217) of a firstovervoltage protection element (210) is greater than the capacitancevalue of the corresponding capacitor (216, 217) of a second overvoltageprotection element (210),

wherein the first overvoltage protection element (210) is assigned to atransistor (111) which is arranged nearer to the input terminal (101) inthe stack (110) than the transistor (111) to which the secondovervoltage protection element (210) is assigned.

EXAMPLE 12

Switch (100) according to Example 9, wherein the capacitance values ofcorresponding capacitors (216, 217) of the overvoltage protectionelements (210) are all the smaller, the further away from the inputterminal (101) the respectively assigned transistors (111) are arrangedin the stack (110).

EXAMPLE 13

Switch (100) according to Example 9,

wherein each overvoltage protection element (210) comprises at least onecapacitor (216, 217),

wherein the capacitance values of corresponding capacitors (216, 217)for overvoltage protection elements (210) assigned to differenttransistors (111) have a deviation with respect to one another of lessthan 50%, preferably less than 20%, particularly preferably less than2%.

EXAMPLE 14

Switch (100) according to Example 1,

wherein each of the at least one overvoltage protection element (210)comprises a capacitor (216) coupled in series with the respectivelyassigned switching element (211) between the gate contact (107) and oneof the source contact (106) and the drain contact (105) of arespectively assigned transistor (111).

EXAMPLE 15

Switch (100) according to Example 14,

wherein each of the at least one overvoltage protection element (210)comprises a further capacitor (217) coupled between the gate contact(107) and the other of the source contact (106) and the drain contact(105) of the respectively assigned transistor (111).

EXAMPLE 16

Switch (100) according to Example 15,

wherein for each of the at least one overvoltage protection element(210) the capacitance value of the respective capacitor (216) is in therange of 60%-140% of the capacitance value of the respective furthercapacitor (217), preferably in the range of 90%-110%, particularlypreferably in the range of 98%-102%.

EXAMPLE 17

Switch (100) according to Example 15,

wherein for each of the at least one overvoltage protection element(210) the capacitance value of the respective capacitor (216) is notless than 1 pF, optionally not less than 2 pF, further optionally notless than 10 pF, and/or wherein for each of the at least one overvoltageprotection element (210) the capacitance value of the respective furthercapacitor (217) is not less than 100 nF, optionally not less than 1 pF,further optionally not less than 500 pF.

EXAMPLE 18

Switch (100) according to Example 1, wherein

each of the at least one switching element (211) comprises a furthertransistor.

EXAMPLE 19

Switch (100) according to Example 1,

wherein the transistors (111) and/or the at least one switching element(211) comprise(s) field effect transistors.

EXAMPLE 20

System comprising:

-   -   the switch (100) according to any of the preceding examples,    -   an LC resonant circuit which is coupled to the input terminal        (101) of the switch (100),    -   a ground contact, which is coupled to the output terminal (102)        of the switch (100).

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. A switch, comprising: an input terminal; anoutput terminal; a stack comprising transistors coupled in series, thestack being coupled between the input terminal and the output terminal;at least one switching element configured to be selectively operated ina conducting state or a non-conducting state; and at least oneovervoltage protection element coupled to the stack by the at least oneswitching element, wherein each one of the at least one overvoltageprotection element comprises: a capacitor coupled in series with arespectively assigned switching element between a gate contact and oneof a source contact and a drain contact of a respectively assignedtransistor; and a further capacitor coupled between the gate contact andthe other one of the source contact and the drain contact of therespectively assigned transistor.
 2. The switch of claim 1, furthercomprising: a supply terminal configured to provide a supply voltage,wherein the at least one switching element is operated in the conductingstate or in the non-conducting state depending on a value of the supplyvoltage.
 3. The switch of claim 2, wherein the at least one switchingelement is configured to be operated in the conducting state if themagnitude of the value of the supply voltage exceeds a predefinedthreshold value.
 4. An integrated circuit comprising the switch of claim2 and a plurality of components coupled to the supply terminal andconfigured to be operated by the supply voltage.
 5. The switch of claim1, wherein the at least one switching element is configured to beoperated in the conducting state or in the non-conducting statedepending on an operating mode of the switch.
 6. The switch of claim 5,further comprising: a user interface configured to determine theoperating mode by user input.
 7. The switch of claim 1, wherein the atleast one switching element is configured to be operated in theconducting state or in the non-conducting state depending on aradio-frequency signal at the input terminal.
 8. The switch of claim 1,wherein the at least one overvoltage protection element is at leastcoupled to the transistor arranged adjacent to the input terminal in thestack.
 9. The switch of claim 1, wherein for each one of the at leastone overvoltage protection element the capacitance value of therespective capacitor is in the range of 60%-140% of the capacitancevalue of the respective further capacitor.
 10. The switch of claim 1,wherein for each one of the at least one overvoltage protection elementthe capacitance value of the respective capacitor is not less than 1 pF,and/or wherein for each of the at least one overvoltage protectionelement the capacitance value of the respective further capacitor is notless than 100 nF.
 11. The switch of claim 1, wherein each one of the atleast one switching element comprises a further transistor.
 12. Theswitch of claim 1, wherein at least one of the transistors and the atleast one switching element comprise field effect transistors.
 13. Asystem, comprising: a switch comprising an input terminal, an outputterminal, a stack comprising transistors coupled in series between theinput terminal and the output terminal, at least one switching elementconfigured to be selectively operated in a conducting state or anon-conducting state, and at least one overvoltage protection elementcoupled to the stack by the at least one switching element; an LCresonant circuit coupled to the input terminal of the switch; and aground contact coupled to the output terminal of the switch.
 14. Amethod, comprising: providing a switch that comprises an input terminal,an output terminal, a stack comprising transistors coupled in series,the stack being coupled between the input terminal and the outputterminal, at least one switching element configured to be selectivelyoperated in a conducting state or a non-conducting state, and at leastone overvoltage protection element coupled to the stack by the at leastone switching element; and selectively activating, using the at leastone switching element, the at least one overvoltage protection elementdepending on at least one of the following: a value of a supply voltage;an operating mode of the switch; a user input received via a userinterface; and a radio-frequency signal provided at the input terminal.15. A switch, comprising: an input terminal; an output terminal; a stackcomprising transistors coupled in series, the stack being coupledbetween the input terminal and the output terminal; a plurality ofswitching elements configured to be selectively operated in a conductingstate or a non-conducting state; and a plurality of overvoltageprotection elements, each overvoltage protection element of theplurality of overvoltage protection elements being coupled to arespectively assigned transistor of the stack by a correspondingswitching element of the plurality of switching elements, wherein: eachovervoltage protection element of the plurality of overvoltageprotection elements comprises at least one capacitor and the capacitancevalues of corresponding capacitors of the overvoltage protectionelements assigned to different transistors have a deviation with respectto one another of more than 50%; and/or the capacitance value of thecapacitor of a first overvoltage protection element of the plurality ofovervoltage protection elements is greater than the capacitance value ofthe corresponding capacitor of a second overvoltage protection elementof the plurality of overvoltage protection elements, and the firstovervoltage protection element is assigned to a transistor of the stackwhich is arranged nearer to the input terminal in the stack than thetransistor of the stack to which the second overvoltage protectionelement is assigned; and/or the capacitance values of correspondingcapacitors of the plurality of overvoltage protection elements aresmaller the further away from the input terminal the respectivelyassigned transistors are arranged in the stack; and/or the capacitancevalues of corresponding capacitors for overvoltage protection elementsof the plurality of overvoltage protection elements assigned todifferent transistors have a deviation with respect to one another ofless than 2%.
 16. A switch, comprising: an input terminal; an outputterminal; a stack comprising transistors coupled in series, the stackbeing coupled between the input terminal and the output terminal; atleast one switching element configured to be selectively operated in aconducting state or a non-conducting state; and at least one overvoltageprotection element coupled to the stack by the at least one switchingelement, wherein the at least one switching element is configured to beoperated in the conducting state or in the non-conducting statedepending on a radio-frequency signal at the input terminal.